A recombinant hepatitis B virus vaccine (Recombivax HB) has been available for human use since 1986. This vaccine consists of 20 nanometer particles which are exclusively made up of hepatitis B virus surface protein (HBS) and has been proven to efficiently elicit hepatitis B virus (HBV) neutralizing antibodies. Subsequently it became evident that an additional amino acid sequence, which is an NH.sub.2 -terminal extension of the HBS protein known as PreS2, was also important in HBV immunity. It was then thought that including PreS2 in a HBV vaccine could have beneficial effects.
A second generation HBV vaccine consisting of recombinant hepatitis B virus PreS2+S antigen (PreS2+S) is currently being developed for use in humans. Antibodies generated against the PreS2 region of the PreS2+S antigen have been shown to block infectivity of HBV. The PreS2 region of the protein has been recently demonstrated to contain immunodominant epitopes for the generation of HBV neutralizing antibodies. The importance of antibodies to the PreS2 region in the course of human disease is underscored by a direct correlation of the. presence of anti Pre-S2 antibodies with convalescence from hepatitis B virus (HBV) infection.
Following vaccination with the recombinant PreS2+S antigen the patient's ability to achieve a high titer of anti PreS2 antibodies will, in turn, directly correlate with protection from HBV infection or minimization of disease. It is therefore essential that the antibody response to PreS2 is assayed without interference from anti-S antibodies, despite the fact that PreS2 and S are parts of one continuous peptide.
Currently, assay systems are available for the detection of anti-PreS2 antibodies. Many of these assays incorporate the PreS2 epitope in the form of short synthetic peptides comprising parts or all of PreS2. Small peptides or fragments of larger proteins may not present an appropriate structural conformation for maximal antibody recognition and may therefore misrepresent natural antigen-antibody interaction.
Furthermore, these assay systems employ as the mode of detection, a radiolabelled or enzyme conjugated antibody specific for antibodies of the test sample source, e.g. .sup.125 I-labelled or alkaline phosphatase-conjugated anti-human IgG, for detecting anti-PreS2 antibodies in human serum. This can lead to increased background interference due to: i) non-specific interactions with antibodies in the test sample which are not specific for PreS2; ii) non-specific interactions of the labelled detector antibody with components of the assay apparatus, and; iii) specific interactions of the labelled detector antibody with antibodies from the test sample which are non-specifically adsorbed to the assay apparatus.